Answer: A semi-permeable membrane is that which only allows certain
substances to pass through.
Quickly... this is a harder one, because all of possible answers are the result of interactions over a long time. However, these change the surface of the earth the fastest
1.) Volcanoes
2.) Flooding
Over a long time
1.) Through the rock cycle... earthquakes, mountain forming, etc.
2.) Melting, or forming of ice... changes sea levels
The chemical formula for water is H2O which means that every molecule of water has 2 atoms of hydrogen (H) and one atom of oxygen (O). Here comes the key part. From the Periodic Table of Elements, one sees that one molecule of oxygen atoms weigh 16 grams.
I apologize if this is not what you meant. If you have further questions just tell me.